Karplus strong

Discuss John Bowen Synths - Solaris
John Bowen
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Re: Karplus strong

Post by John Bowen » Mon Jun 17, 2013 6:33 am

I'd like to make another small point about these presets - and any presets where you want to use the output from a final VCA for some kind of control or modulating signal - that you don't need to have the Enable Part switch ON for it to work. This only mutes the Part in the final output (Synth) mix. So, for most of your Presets, you have Part 1 Enabled, but if you listen to only Part 1 by itself, you hear very faintly the little noise burst, and this is not a needed element to put into the final mix; it is used earlier in the signal path. (Of course, you CAN leave it in the audio path at the end, but disabling the Part with the switches does not remove it from the Mod Source and Signal Source paths.)

Elhardt
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Re: Karplus strong

Post by Elhardt » Tue Feb 18, 2014 6:45 am

Hello. I'm Ken Elhardt and saw my name brought up in regards to this thread. I don't know if people get email notifications or whether my post will go unnoticed, but I just randomly dropped by here and saw this thread. Let me clear up some of the confusion. When I had a Solaris here to program patches on, all 4 of the comb filters appeared to have negative feedback or were inverting the sound somewhere within the comb filter. That was one of the bugs I reported to John Bowen. Since that appears to have been forgotten, then that probably means it hasn't been fixed. Karplus Strong as far as I know wants a positive feedback loop. I can't remember whether I tried to setup a KS patch or not, or just happened to notice all comb filters seemed inappropriate for the task. That's not to say you won't get some kind of sound out of KS using negative feedback delay lines, but it may not give the results expected.

I did use some comb filters in some of my patches, but also used the built in digital delay (or was it the chorus, can't remember) for some comb filtering too IIRC. Using comb filters with negative feedback or negating the sound at some point within the comb filter results in a hollow sound (like a square wave) and all 4 Solaris comb filters had that hollow sound. To confirm visually that this is the case with the Solaris, you could set the comb filters to something like 1 ms (assuming they can be set based on ms or seconds) and turn the resonance up a bit, then run white noise through them and record to an audio file, then examine in an audio editor app that can display an FFT. You should see a series of peaks starting at 1000 Hz and spaced 1000 Hz appart like --> 1000 2000 3000 4000 and so on, in other words a natural harmonic series. If the comb filter is negating the signal at some point, you will instead see notches at 1000 2000 3000 4000 Hz, and so on. That means you'll see peaks in between those frequencies at 1500 2500 3500 Hz, and so on. That is not a natural harmonic series and produces a hollow sound.

Makes me wonder if the messed up voltage controlled envelope generators I pointed out to John were fixed or not, or any other bugs I reported.

John Bowen
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Re: Karplus strong

Post by John Bowen » Tue Feb 18, 2014 10:15 am

Ken, as I have mentioned here, the coder said that he needs to add an additional mode to the Comb filter model to work correctly for K/S. I quite appreciate your clarification in your post, but don't think he saw the current models as having a bug; rather that he just didn't program the mode needed to do proper K/S.
John Bowen wrote:So, we had our meeting yesterday, and Klaus states the best way to solve this will be to add another Mode to the Comb filter. I'm not sure when he can do this, but I am sure this will be easier to implement here.

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